An example of a conventional vibration damping device configured to reduce torque fluctuations of a rotary member and to dampen torsional vibrations of the rotary member resulting from the torque fluctuations is disclosed in Japanese Patent Laid-Open No. 2002-13547. In order to reduce the torque fluctuations and to dampen the torsional vibrations, the vibration damping device taught by Japanese Patent Laid-Open No. 2002-13547 is attached to a crank shaft of an engine of a vehicle, an input shaft of a transmission, a drive shaft and so on.
The vibration damping device taught by Japanese Patent Laid-Open No. 2002-13547 is arranged on a rotary shaft between an engine and a transmission for changing a speed derived from a power generated by the engine. The rotary shaft on which the vibration damping device is thus arranged includes an output shaft of the engine and an input shaft of the transmission connected therewith in a power transmittable manner. The vibration damping device taught by Japanese Patent Laid-Open No. 2002-13547 is provided with: a first inertial body adapted to absorb the torque fluctuations and the torsional vibrations by an inertia force; a torque limiter mechanism connected with the first inertial body and arranged closer to the transmission than the first inertial body; and a torsion mechanism, which is connected with the torque limiter mechanism in a power transmittable manner and arranged closer to the transmission than the torque limiter mechanism, and which is configured to absorb or dampen the torque fluctuations and the torsional vibrations by the inertia force of an elastic member thereof. Specifically, the torsion mechanism is arranged inside of the torque limiter mechanism in a radial direction of the rotary shaft, and connected with a member rotated integrally with the rotary shaft which is provided with a second inertial body. The torque limiter mechanism is configured to limit a power transmission between the output shaft and the input shaft in case torque therebetween is increased to a certain extent.
Thus, the vibration damping device taught by Japanese Patent Laid-Open No. 2002-13547 is configured to reduce or dampen the torque fluctuation and the torsional vibrations of the rotary member by the inertia forces of the first and the second inertial bodies, and the elastic force of the elastic member of the torsion mechanism. In order to enhance the vibration damping ability, for example, it may be effective to substitute the second inertial body with a pendulum damper comprising a pendulum adapted to reduce the torque fluctuation and to dampen the torsional vibrations by an oscillating motion thereof resulting from the torque fluctuation and the torsional vibrations.
However, the torque limiter mechanism may structurally cause a misalignment between a rotational center of the output shaft arranged in the engine side (i.e., a drive side) of the torque limiter mechanism, and a rotational center of the input shaft arranged in the transmission side (i.e., a driven side) across the torque limiter mechanism. Therefore, if the vibration damping device taught by Japanese Patent Laid-Open No. 2002-13547 is modified to enhance the vibration damping ability as described above, a rotational center of the pendulum damper may be decentered with respect to the rotational center of the output shaft.
If the rotational center of the pendulum damper is decentered with respect to the rotational center of the output shaft, a distance between the rotational center of the output shaft and a fulcrum of oscillation of the pendulum is varied. Consequently, an order frequency of the oscillating motion of the pendulum is changed by such decentering of the rotational center of the pendulum damper. In this case, the vibration damping ability of the pendulum damper and the vibration damping device may be degraded.
Alternatively, it is also considerable to substitute the first inertial body of the vibration damping device taught by Japanese Patent Laid-Open No. 2002-13547 with the pendulum damper. However, if such modification is carried out, power of the engine is inputted directly to the pendulum damper. Therefore, durability and the damping ability of the pendulum damper may be degraded.